Semiconductor package assembly and method for electrically isolating modules

ABSTRACT

A semiconductor package assembly and method for electrically isolating modules, having a capacitor within the semiconductor package assembly. The package assembly and method are suitable for electrically isolating modules according to IEEE 1394.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of pending U.S. patent application No.10/675,965, filed Sep. 30, 2003.

TECHNICAL FIELD

The present invention relates to semiconductor device packaging, andmore particularly, to electrically isolating semiconductors within apackage assembly.

BACKGROUND OF THE INVENTION

Computers are routinely used to receive and process data from peripheraldevices such as digital cameras and digital video recorders. Theperipheral devices typically transfer data to a computer via a serialbus. Viewing images captured by these peripheral devices in real-time,for example, requires the peripheral device to transfer a relativelylarge amount of data to the computer in a relatively short amount oftime. In the past, computers used a Universal Serial Bus (“USB”) totransfer such data, but a USB cannot guarantee real-time viewing ofdigital transmissions due to its inherent limitations. Thus, the IEEE1394 standard was developed to allow simple, low-cost, high-bandwidth,real-time data interfacing between computers and peripherals withoutsignificant signal degradation.

IEEE 1394 is a nonproprietary, high-speed, serial bus input/outputstandard. It provides a comprehensive standard for connecting digitaldevices, including personal computers and consumer electronics hardware.It is also platform-independent, scalable (expandable), and flexible insupporting peer-to-peer (roughly, device-to-device) connections. IEEE1394 preserves data integrity by eliminating the need to convert digitalsignals into analog signals. Created for desktop networks by AppleComputer, which called the technology FIREWIRE™, and further, developedby the IEEE 1394 working group, it is considered a low-cost interfacefor devices such as digital cameras, camcorders, and multimedia devices.In addition, it is seen as a means of integrating personal computers andhome electronics equipment.

FIG. 1 illustrates peer-to-peer connections according to the IEEE 1394standard. A computer 102 in a room 104 is communicatively coupled to acomputer 106 in a room 108 via a serial bus 105. Another serial bus 109is used to communicatively couple the computer 106 to another computer110 in another room 112. Each computer on the network includesnetworking components that implement IEEE 1394.

FIG. 2 illustrates the IEEE 1394 networking components 200 that includea physical layer chip (“PHY”) 202 and a link layer chip (“LINK”) 204.The LINK chip 204 contains the networking intelligence to process andgenerate networking signals, such as arbitration signals and packets.The PHY chip 202 is the physical interface by which the computer systemmay receive or send networking information to and from the serial bus.The PHY chip 202 also serializes the data from the LINK chip 204 if thedata is to be sent out to the serial bus 220, and likewise deserializesthe data from the cable to be sent to the LINK chip 204 in parallelformat. There are typically at least fourteen wires that communicativelycouple the PHY chip 202 to the LINK chip 204.

IEEE 1394 specifies that all devices connected to a serial bus have thesame reference ground potential as provided by the ground wire of theserial bus. IEEE 1394 recognizes, however, that separate devicesconnected to the bus may have different ground potentials. Such voltagedifferences could result in direct current flowing from the devicehaving the higher ground potential to the device having the lower groundpotential. Not only could such a current flow cause signal degradation,but it could cause damage to circuitry within the device as well. Thus,IEEE 1394 recommends that the ground wire of the serial bus beelectrically isolated from the rest of the networking components inorder that all PHY chips connected to a serial bus operate on the sameisolated ground domain.

FIG. 2 illustrates the recommended arrangement for electrical isolationof the PHY 202 and LINK 204 networking components. The ground 216 of theLINK chip 204 is coupled to the computer's chassis (not shown) as areference. The ground 212 of the PHY chip is coupled to the ground 213of the serial bus 220. A parallel configuration of a capacitor 208 and aresistor 206 effectively isolate the ground 213 of the serial bus 220from the ground 216 of the LINK chip 204. The PHY and LINK chips arecommunicatively coupled by capacitors 214 ₁₋₁₄.

This approach works well, but it is incompatible with the trend toreduce the size of electronic devices. Two major reasons account for thedesire to decrease the size, shape, and configuration of electronicdevices. First, smaller footprint circuitry allows a reduction in thetrace lines that go from any pin on an integrated circuit package to thepad on a die, helping to increase signal integrity. Second, smallercomponents occupy less space on a printed circuit board, thus allowingmore room for other useful components on the same printed circuit board.Hence, the solution offered by IEEE 1394 using an external capacitor andresistor to electrically isolate the PHY and LINK chips createsunnecessary bulkiness through use of additional electronic components.And while combined PHY-LINK chips are commercially available, such chipsoperate on the same ground potential and thus are unsuitable fordistributed systems where differences in ground potential may exist.Thus, there is a need for structures for connecting digital deviceswhile isolating them from undesired direct current while also conformingwith the trend toward miniaturization of electronic devices.

SUMMARY OF THE INVENTION

The present invention is directed to electronic module packages having acapacitor incorporated within the package for electrically isolating themodules. The resulting package requires less external electroniccomponents than the assemblies currently employed to electricallyisolate modules. The present invention is further directed to methodsfor electrically isolating modules within a package assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial diagram showing a conventional network in abuilding.

FIG. 2 is a block diagram of conventional networking componentsaccording to IEEE 1394.

FIG. 3 is a cross-sectional view of a package assembly according to oneembodiment of the present invention.

FIG. 4 is a cross-sectional view of a package assembly according toanother embodiment of the present invention.

FIG. 5 is a cross-sectional view of a package assembly according toanother embodiment of the present invention.

FIG. 6 is a cross-sectional view of a package assembly according to yetanother embodiment of the present invention.

FIG. 7 is a cross-sectional view of a package assembly according toanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As previously mentioned, there is a general trend within the electronicsindustry towards miniaturization of components such as semiconductorpackages. Miniaturization is aided by consolidating various componentsinto a single package. Not only will such a single-package arrangementtypically be smaller, but it will ordinarily result in lowermanufacturing costs. Embodiments of the present invention includesemiconductor package assemblies incorporating a capacitor within theassembly to electrically isolate modules.

Methods and materials for manufacturing semiconductor package assembliesare well-known in the art. Semiconductor devices are typicallyfabricated on thin wafers of silicon. Several dice are produced on eachwafer, with each die representing a single semiconductor device. Eachdie on a wafer is tested for gross functionality, and sorted accordingto whether the die passes or fails the gross functionality test. Afterbeing sorted according to gross functionality, the wafers are cut usinga wafer saw, and the individual die are singulated. The die determinedto be non-functional are scrapped. The functional die are packaged andfurther tested to ensure that each packaged device satisfies a minimumlevel of performance. Typically, the functional devices are permanentlypackaged by encapsulating the die in a non-conductive dielectricmaterial. Packaging of the functional devices facilitates handling ofthe devices and also protects the die from damage during the manufactureof circuits using the packaged devices.

Recently, semiconductor manufacturers have developed a package structurewhere unpackaged die are mounted directly onto a substrate, for example,a printed circuit board, thus allowing modules to be designed withincreased device density. Examples of these types of packages structuresinclude ball grid array (BGA) packages, and other chip scale packages(CSP) having package dimensions that are slightly larger than thedimension of the encapsulated die. The die is mounted onto the substrateand is electrically coupled to conductive traces formed on the substrateby wire bonding the bond pads of the die. Alternatively, the conductivetraces and the bond pads may be electrically coupled by using tapeautomated bonded (TAB) wire instead. The resulting structure issubsequently, partially or entirely, encapsulated to protect the devicefrom damage. External leads, often in the form of solder balls, are thenattached to attachment sites on the conductive traces so that theintegrated circuit fabricated on the die may be electrically contactedthrough the external leads.

Following packaging, the device is typically mounted onto a printedcircuit board (PCB) as a component in a larger electronic system.Conductive pads on the PCB are positioned to correspond to the locationof the external leads of the packaged device. The packaged device ispositioned accordingly onto the conductive pads and subjected to areflow process at an elevated temperature in order to solder thepackaged device to the PCB. In the case of a BGA type package, thesolder is provided by the solder balls of the completed package.

FIG. 3 illustrates an example of a package assembly 300 according to oneembodiment of the present invention. A first electronic module 304 and asecond electronic module 305 are attached to a substrate 302. The firstand second modules are communicatively coupled by metallic traces 303 onthe substrate that have capacitors 301 in series to prevent directcurrent from flowing between the modules. A capacitor is formed withinthe package by conductively coupling the ground plane of the firstelectronic module 304 to a first conductive surface 310 below thesubstrate 302, and the ground plane of the second electronic module 305conductively coupled to the second conductive surface 312 that is spacedapart from the first conductive surface 310. The first and secondconductive surfaces 310, 312 are further separated by a dielectric 314.A resistor 308 is coupled between the first and second conductivesurfaces 310, 312 by its first and second terminals respectively toallow the conductive surfaces to equilibrate after power is shut off tothe modules.

One of ordinary skill in the art would readily appreciate that varioussuitable materials may be selected for the package assembly. Forexample, the resistor can be of any size sufficient to store a charge onthe conductive surfaces while in operation and allow the conductivesurfaces to equilibrate after power is shut off. Typically, however,resistance of approximately one megohm is desirable. Similarly, thedielectric may be any suitable non-conductive material. In addition, themodules 304, 305 may be conductively coupled to the conductive surfaces310, 312 in a number of ways, such as with wires 306 bonded between themodules 304, 305, and the conductive surfaces 310, 312, or via metallictraces on the substrate. The particular qualities of the electroniccomponents and the means by which they are coupled to other devices asdescribed above are provided as a non-limiting example of a typicalembodiment in accordance with the present invention, and are notintended to limit the scope of the present invention.

According to IEEE 1394, the first module 304 is a PHY chip conductivelycoupled to a serial bus (not shown) in order to send signals to orreceive signals from another device on the bus. The PHY chip 304 isfurther conductively coupled to the ground wire of the serial bus (notshown). The second electronic module 305 is a LINK chip that iscommunicatively coupled to the PHY chip 304 via a number of capacitorsin series (not shown); the communicative coupling transmits signalsoriginating from the serial bus and processed by the PHY chip 304. TheLINK chip 305 is further conductively coupled to the chassis of thecomputer (not shown) in which it is housed. The PHY 304 and LINK 305chips are each conductively coupled to a first conductive surface 310and second conductive surface 312, respectively. A capacitor is formedwithin the package assembly by the first conductive surface 310 beingconductively coupled to the serial bus ground wire (not shown) andspaced apart by a dielectric from the second conductive surface 312,which is conductively coupled to the chassis ground 216 of the computer(not shown) and the LINK chip 305. A resistor 308 provides a path to thelocal chassis ground in the event a charge is coupled to the serial busground. In addition, when power is shut off to the PHY and LINK chips304, 305, the resistor 308 allows the direct current to flow between thesurfaces 310, 312 to normalize any potential differences between the twosurfaces while preventing too much direct current from damaging thefirst 304 and second 305 modules that are conductively coupled to theconductive surfaces. Although the resistor 308 is depicted as external,one skilled in the art would readily appreciate that the resistors inthe embodiments discussed herein may be integral to the semiconductordevice packages and formed of any suitable material, such as thinresistive film. The particular qualities of the modules and how they arecoupled to other devices as described above are provided as anon-limiting example of an embodiment in accordance with the presentinvention, and are not intended to limit the scope of the presentinvention.

FIG. 4 illustrates a cross sectional view of another embodiment of thepresent invention where first and second integrated circuits 416, 418are incorporated within a single module 404 while remaining electricallyisolated. Methods and materials for manufacturing a single module havingtwo or more semiconductors are well-known in the art, and will not bedescribed in detail herein. A capacitor is formed by the ground pin (notshown) of the first integrated circuit 416 conductively coupled to thefirst conductive surface 410 spaced apart from the second integratedcircuit 418 conductively coupled by its ground pin (not shown) to thesecond conductive surface 412 using wires 406 or any other suitableconductive coupling.

FIG. 5 illustrates another embodiment of the present invention where thepackage assembly has electronic modules 504, 505 on separate substrates502, 503 within the assembly. In this embodiment, a first electronicmodule 504 is attached to a first substrate 502 and a second electronicmodule 505 attached to a second substrate 503 are spaced apart by thefirst and second conductive surfaces 510, 512 and the dielectric 514. Aswith other embodiments of the invention, the first and second electronicmodules 504, 505 are conductively coupled to the first and secondconductive surfaces 510, 512 respectively with wire bonds 506 or anyother suitable conductive couplings. A dielectric 514 is interposedbetween the conductive surfaces 510, 512 to prevent direct current fromflowing between the conductive surfaces.

FIG. 6 illustrates yet another embodiment of the present invention,where the capacitor formed by the first and second conductive surfaces610, 612 and dielectric 614 is on the same side of the substrate 602 asthe first and second electronic modules 604, 605. The electronic modules604 605 may also be combined into a single structure as shown in FIG. 4.

FIG. 7 illustrates another embodiment of the invention where the firstand second electronic modules 704, 705 are stacked on the substrate 702,as opposed to both being attached to the substrate as illustrated in,for example, FIGS. 3 and 6. The electronic modules 704, 705 are attachedwith adhesive at the bondline 718. Methods and materials for attachingelectronic modules with adhesives are well-known in the art, and thedetails will not be described in detail herein.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. An integrated circuit package assembly for electrically isolatingintegrated circuits within a module, comprising: a substrate having afirst side and an opposing second side; a module attached to the firstside of the substrate, the module having a first and second integratedcircuits; a first conductive surface adjacent to the second side of thesubstrate, the first conductive surface conductively coupled to thefirst integrated circuit; a second conductive surface spaced apart fromthe first conductive surface to form a capacitor with the firstconductive surface, the second conductive surface being conductivelycoupled to the second integrated circuit; and a plurality of capacitorseach of which is coupled in series between the first integrated circuitand the second integrated circuit, the capacitors being operable tocouple signals processed by the first integrated circuit to the secondintegrated circuit.
 2. The package assembly of claim 1, furthercomprising a dielectric interposed between the first and secondconductive surfaces.
 3. The package assembly of claim 1, furthercomprising an encapsulation substantially surrounding the packageassembly.
 4. The package assembly of claim 2 wherein the packageassembly is encased in a polymer.
 5. The package assembly of claim 2wherein the package assembly is encased in ceramic.
 6. The packageassembly of claim 2 wherein the package assembly is encased in a glass.7. The package assembly of claim 1, further comprising a resistor havinga first terminal coupled to the first conductive surface and furtherhaving a second terminal coupled to the second conductive surface. 8.The package assembly of claim 7 wherein the resistor has a resistance ofapproximately one megohm.
 9. The package assembly of claim 7 wherein theresistor is a resistant film.
 10. The package assembly of claim 1,further comprising a first ground plane connected to the firstconductive surface, and a second ground plane connected to the secondconductive surface.
 11. The package assembly of claim 10 wherein thefirst ground plane comprises a ground wire of a cable bus.
 12. Thepackage assembly of claim 10 wherein the second ground plane comprises achassis of a computer.